In food processing and other commercial applications, the use of microbial or fungal enzymes adsorbed onto or bonded to inert carriers to provide immobilized biological catalysts has largely superseded older methods wherein soluble enzymes or whole cells of microorganisms were utilized. In general, the use of immobilized enzymes provides a number of significant advantages over the older methods. The major advantage is that the immobilized enzymes are adaptable for use in continuous conversion processes. Thus, a more efficient use of the enzyme is attained and the contact time between the enzyme and the substrate is reduced, thereby resulting in an improved product quality and a reduction in enzyme and production costs.
Cellulose occurs in nature as a linear polymer comprised of anhydroglucose units joined together by .beta.-1,4 glucosidic bonds. Each anhydroglucose unit contains three free hydroxyl groups capable of reacting with appropriate reagents to form insoluble cellulose derivatives which, due to their inertness, large surface area, and open, porous structure, have a high adsorptive or ion-exchange capacity for protein molecules.
The preparation and utilization of ion exchange enzyme adsorbents derived from cellulose are known in the art. Peterson and Sober, J. A. C. S. 78, 751 (1956) and Guthrie and Bullock, I/EC, 52, 935 (1960) described methods for preparing adsorptive cellulose products which could be utilized to separate or purify enzymes and other proteins. Tsumura et al., Nippon Shakuhin Kogyo Gakkaishi, 14, (12), (1967) disclosed binding glucose isomerase to DEAE-Sephadex.
U.S. Pat. No. 3,708,397 to Sipos relates to a process for immobilizing glucose isomerase on basic anion exchange celluloses. U.S. Pat. No. 3,823,133 to Hurst et al. is directed to a method for preparing cationic cellulose ethers having a high adsorptive capacity for enzymes and other proteinaceous materials. U.S. Pat. No. 3,838,007 to van Velzen sets forth a process in which an enzyme preparation is obtained in particulate form. U.S. Pat. Nos. 3,788,945 and 3,909,354, both to Thompson et al., disclose continuous processes for converting glucose to fructose by passing a glucose-containing solution through fixed or fluidized beds containing glucose isomerase bound to various cellulose products. U.S. Pat. No. 3,947,325 to Dinelli et al. is directed to the preparation of cellulose-containing englobed enzymatic material. The cellulose is formed from an emulsion comprising an aqueous enzyme solution and nitrocellulose. U.S. Pat. No. 3,956,065 to Idaszak et al. is concerned with a continuous process for converting glucose to fructose whereby a glucose-containing solution is passed through a bed comprising a cellulose derivative having glucose isomerase immobilized thereon and non-porous or granular polystyrene beads. The beads inhibit packing and channeling of the bed when such is used in flow reactors. Peska et al., in an article entitled "Ion Exchange Derivatives of Bead Cellulose", Die Angewandte Makromolekulare Chemie, 53, pp. 73-80, (1976), described several derivatized celluloses prepared in bead form.
U.S. Pat. Nos. 4,110,164 and 4,168,250, both to Sutthoff et al., relate to agglomerated fibrous ion exchange cellulose composites and processes for preparing the same. In these processes a hydrophobic polymer is combined with fibrous (rather than granular) cellulose which has previously been derivatized to impart ion exchange properties thereto. Although these composites perform satisfactorily in a number of applications, their ion exchange capability and capacity for adsorbing or binding glucose isomerase are not as great as desired. Moreover, the economics of these processes are such as to make the production of the composites more costly than is preferred.
U.S. Pat. No. 4,355,117 to Antrim et al. provides a process for preparing an agglomerated DEAE-cellulose composite which overcomes many of the shortcomings discussed above and is the preferred process for preparing the composite useful in practicing this invention.
U.S. Pat. Nos.4,205,127 to Fujita et al. teaches the use of an aqueous salt solution at 50.degree.-75.degree. C. to desorb spent enzyme from synthetic anion exchange resins such as styrene-divinyl benzene resin (Column 1, lines 39-59). Fujita does not disclose the use of any cellulosic resins.
Japanese patent publication 31075/1979 teaches that DEAE-cellulose may be used as a support for glucoamylase. The enzyme is added to the support from an aqueous solution until swelling equilbrium is reached.
U.S. Pat. No. 3,234,199 to Reid uses a mixture of cationic and anionic exchange resins in a protein fractionation process. None of the Reid resins are cellulosic. Further, Reod washes his resins so as to specifically avoid the use of elevated temperatures (Column 3, lines 49-52).